A video encoder compresses video information so that more information can be sent over a given bandwidth. The compressed signal may then be transmitted to a receiver that decodes or decompresses the signal prior to display.
Rate control often used to control the number of generated bits for various video applications. Usually, the application provides a target bit rate and buffer constraint to the rate control module. The rate control module may use this information to control the encoding process such that target bit rate is met and buffer constraint is not violated.
Such a target bit rate oriented approach may waste bits when the video quality is already very good. In order to solve this problem, one solution is to use a constant minimum quantization parameter (QP) to cap the QP generated by the rate control module.
Similarly, Rate Distortion Optimized Quantization (RDOQ) often improves the coding efficiency (e.g., Bjøntegaard-Delta (BD) Rate) for many video codec (e.g., Advanced Video Coding (AVC), High Efficiency Video Coding (HEVC), etc.). Such an RDOQ is often set at the frame level.
For example, Rate Distortion Optimized Quantization (RDOQ) is typically part of quantization operations in an encoder (e.g., JPEG, MPEG2, AVC, HEVC, VP9, and AV1 etc.). RDOQ typically determines the optimal quantization level of each transform coefficient among multiple quantization level candidates by minimizing the sum of rate distortion costs in each block.